Add link to Windows Phone wallet app

reddit user [/u/Zumicts](http://www.reddit.com/user/Zumicts) made a Windows Phone app that uses DogeAPI.

Found in [this post to /r/dogecoin](http://www.reddit.com/r/dogecoin/comments/29dmug/reposting_from_rwindowsphone_a_mobile_wallet_for/)